The present invention relates to an ink jet head mounted in an ink jet recording apparatus for ejecting ink drops and, more particularly, to an ink jet head of the type which uses a piezoelectric high molecular substance to form an element for compressing ink in an ink chamber.
Various types of ink jet heads have been proposed for use with an ink jet recording apparatus. Typical of such ink jet heads is one which utilizes a ceramic piezoelectric element as the element for compressing ink in an ink chamber. The problem with this type of ink jet head is that the piezoelectric element and, therefore, an ink compressing section where the piezoelectric element is positioned occupies a substantial area to obstruct a multi-head, or multi-nozzle, construction. The other ink jet heads heretofore proposed include one which relies on the effect of an electric field or that of a magnetic field, and one which utilizes bubbles. The electric or magnetic field type ink jet head, however, requires relatively high drive voltage for operation and, therefore, its associated drive circuit cannot be reduced in size beyond a certain limit. The bubble type ink jet head, on the other hand, is poor in durability because it has to repeatedly produce bubbles by thermal pulses.
Generally, an ink jet head is constructed to eject ink drops by reducing the volume of an ink chamber in response to print signals, i.e., by compressing ink in the ink chamber. An attempt has recently been made to use a piezoelectric high molecular substance to form ink compressing means of the ink jet head. The piezoelectric high molecular substance is often selected from copolymers including polyvinylidene fluoride, polyvinyl fluoride, polyvinyl chloride, vinylidene fluoride and ethylene trifluoride (Poly-VDF.TrFE), high molecular compound piezoelectric substances such as PVDF/PZT, rubber/PZT, polyacetal/rubber/PZT and epoxy/PZT, etc. These piezoelectric high molecular substances are effectively usable as a material of an ink compressing element of an ink jet head due to their advantageous physical properties such as flexibility, desirable adaptation to a curved configuration, ease of shaping in a thin film and increasing in size, and light weight. In contrast, inorganic piezoelectric elements are hard and quite susceptible to dynamic changes.